The present application relates to an image pickup apparatus, and more particularly to an image pickup apparatus which is suitable for obtaining an image from an electromagnetic wave such as an infrared ray.
Heretofore, an infrared image pickup apparatus (such as a thermography) which captures an image of an object by using an infrared sensor composed of pixels each adapted to detect an infrared ray, thereby measuring a temperature of the object as an object whose image is to be captured has been proposed. This infrared image pickup apparatus, for example, is described in Japanese Patent Laid-Open No. 2004-317152.
The infrared image pickup apparatus is composed of a lens and an image pickup element. In this case, very expensive devices are used as these two constituent elements, respectively. A very expensive lens group made of germanium (Ge), zinc sulfide (ZnS), silicon (Si) or the like which has an excellent transmittance in an infrared wavelength region needs to be used as the lens.
For example, a price of one sheet of Ge lens is 10,000 to 50,000 yen. Also, two to five sheets of Ge lenses are used as one set. For this reason, although depending on the necessary resolution, the cost of only the lens group becomes 20,000 to 250,000 yen in total.
Germanium used in the existing Ge lens is a rare metal. Thus, since the flows of germanium in the market are very small, a unit price of the material is as very expensive as 50,000 to 180,000 yen/kg.
It is expected that more inexpensive zinc sulfide (ZnS), for example, is used as an alternate material. However, although ZnS is inexpensive in its unit price of the material, a processing cost is costly because its processing productivity is poor. As a result, the price of the ZnS lens does not change from that of the Ge lens so much.
Although the Si lens is more inexpensive than the Ge lens, the Si lens is unsuitable for being used in the thermography because a transmittance thereof in a far-infrared region (8 to 14 μm) is inferior.
Therefore, the lens which is inexpensive and is not inferior in transmittance without using the rare metal is not currently realized. As has been described, the inexpensive lens is not yet proposed in the image pickup apparatus for the general terahertz wave typified by the far-infrared thermography.
On the other hand, the image pickup element has a hollow structure, called a micro-bolometer, in which pixels each made of a vanadium oxide (VOx) are individually supported in the air.
The reason for requiring the hollow structure is as follows: An S/N ratio of a signal level to a noise level caused by self-heating or the like of a circuit system is poor because of a heated infrared sensor and a low sensitivity of the VOx element. Thus, for heat insulation, the hollow structure is forced to be adopted in the image pickup element.
For this reason, the micro-bolometer is very poor in productivity and thus is a very expensive device.
Vanadium in VOx is a rare metal, the number of manufacturing processes for manufacturing the hollow structure is increased, and thus the manufacturing cost is increased. This causes the micro-bolometer to be expensive.
Under present circumstances, due to the very expensive structure described above, the price in terms of the infrared image pickup apparatus is about 600,000 yen in a low pixel product, and is about 9,000,000 yen in a high pixel product. For this reason, the infrared image pickup apparatus only for business-oriented market is a commercial reality, and thus the infrared image pickup apparatus does not reach an increase in the market in terms of the consumer.
The terahertz wave image pickup apparatus other than the far-infrared thermography also undergoes the same situation as that of the thermography and thus is more expensive than the thermography.
The use application of the current far-infrared thermography is merely limited to industrial equipment temperature management, object temperature detection for defense/security, night vision for night human body detection used for a luxury class car, and medical body temperature detection. Also, the worldwide shipping volume of the far-infrared thermography is 10,000 to 20,000 yen at the most.
In addition, the fact is that the image pickup apparatus for the terahertz wave is hardly produced.
For structuring cheaply the infrared sensor as compared with the image pickup apparatus such as the existing infrared image pickup apparatus (such as the thermography) or the existing teraheltz-wave image pickup apparatus, for example, it is expected to use a charge collecting element. An automatic door, an air conditioner, a human body detecting sensor for detecting that there is a human body in front of a TV, or the like is given as an example in which the charge collecting element is used in the use application of the far-infrared detection.